[PATCH] mm/damon: Use set_huge_pte_at() to make huge pte old

[PATCH] mm/damon: Use set_huge_pte_at() to make huge pte old

[Baolin Wang]

The huge_ptep_set_access_flags() can not make the huge pte old according
to the discussion [1], that means we will always mornitor the young state
of the hugetlb though we stopped accessing the hugetlb, as a result DAMON
will get inaccurate accessing statistics.

So changing to use set_huge_pte_at() to make the huge pte old to fix this
issue.

[1] https://lore.kernel.org/all/Yqy97gXI4Nqb7dYo@arm.com/

Fixes: 49f4203aae06 ("mm/damon: add access checking for hugetlb pages")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 mm/damon/vaddr.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 5767be72c181..d24148a8149f 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -337,8 +337,7 @@ static void damon_hugetlb_mkold(pte_t *pte, struct mm_struct *mm,
 	if (pte_young(entry)) {
 		referenced = true;
 		entry = pte_mkold(entry);
-		huge_ptep_set_access_flags(vma, addr, pte, entry,
-					   vma->vm_flags & VM_WRITE);
+		set_huge_pte_at(mm, addr, pte, entry);
 	}
 
 #ifdef CONFIG_MMU_NOTIFIER
-- 
2.27.0

Re: [PATCH] mm/damon: Use set_huge_pte_at() to make huge pte old

[SeongJae Park]

Hi Baolin,

On Mon, 20 Jun 2022 10:34:42 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote:

> The huge_ptep_set_access_flags() can not make the huge pte old according
> to the discussion [1], that means we will always mornitor the young state
> of the hugetlb though we stopped accessing the hugetlb, as a result DAMON
> will get inaccurate accessing statistics.
> 
> So changing to use set_huge_pte_at() to make the huge pte old to fix this
> issue.
> 
> [1] https://lore.kernel.org/all/Yqy97gXI4Nqb7dYo@arm.com/
> 
> Fixes: 49f4203aae06 ("mm/damon: add access checking for hugetlb pages")

As the commit has merged in from v5.17, I guess it would be better to do below?

Cc: <stable@vger.kernel.org>

> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>

Other than that,

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

> ---
>  mm/damon/vaddr.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> index 5767be72c181..d24148a8149f 100644
> --- a/mm/damon/vaddr.c
> +++ b/mm/damon/vaddr.c
> @@ -337,8 +337,7 @@ static void damon_hugetlb_mkold(pte_t *pte, struct mm_struct *mm,
>  	if (pte_young(entry)) {
>  		referenced = true;
>  		entry = pte_mkold(entry);
> -		huge_ptep_set_access_flags(vma, addr, pte, entry,
> -					   vma->vm_flags & VM_WRITE);
> +		set_huge_pte_at(mm, addr, pte, entry);
>  	}
>  
>  #ifdef CONFIG_MMU_NOTIFIER
> -- 
> 2.27.0

Re: [PATCH] mm/damon: Use set_huge_pte_at() to make huge pte old

[Baolin Wang]

Hi SeongJae,

On 6/21/2022 1:27 AM, SeongJae Park wrote:
> Hi Baolin,
> 
> On Mon, 20 Jun 2022 10:34:42 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote:
> 
>> The huge_ptep_set_access_flags() can not make the huge pte old according
>> to the discussion [1], that means we will always mornitor the young state
>> of the hugetlb though we stopped accessing the hugetlb, as a result DAMON
>> will get inaccurate accessing statistics.
>>
>> So changing to use set_huge_pte_at() to make the huge pte old to fix this
>> issue.
>>
>> [1] https://lore.kernel.org/all/Yqy97gXI4Nqb7dYo@arm.com/
>>
>> Fixes: 49f4203aae06 ("mm/damon: add access checking for hugetlb pages")
> 
> As the commit has merged in from v5.17, I guess it would be better to do below?
> 
> Cc: <stable@vger.kernel.org>

Yes, thanks for reminding. Hope Andrew can help to add the stable tag 
when picking up this patch.

> 
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> 
> Other than that,
> 
> Reviewed-by: SeongJae Park <sj@kernel.org>

Thanks.

Re: [PATCH] mm/damon: Use set_huge_pte_at() to make huge pte old

[Mike Kravetz]

On 06/20/22 10:34, Baolin Wang wrote:
> The huge_ptep_set_access_flags() can not make the huge pte old according
> to the discussion [1], that means we will always mornitor the young state
> of the hugetlb though we stopped accessing the hugetlb, as a result DAMON
> will get inaccurate accessing statistics.
> 
> So changing to use set_huge_pte_at() to make the huge pte old to fix this
> issue.
> 
> [1] https://lore.kernel.org/all/Yqy97gXI4Nqb7dYo@arm.com/
> 
> Fixes: 49f4203aae06 ("mm/damon: add access checking for hugetlb pages")
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>

Thanks,

Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz

> ---
>  mm/damon/vaddr.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> index 5767be72c181..d24148a8149f 100644
> --- a/mm/damon/vaddr.c
> +++ b/mm/damon/vaddr.c
> @@ -337,8 +337,7 @@ static void damon_hugetlb_mkold(pte_t *pte, struct mm_struct *mm,
>  	if (pte_young(entry)) {
>  		referenced = true;
>  		entry = pte_mkold(entry);
> -		huge_ptep_set_access_flags(vma, addr, pte, entry,
> -					   vma->vm_flags & VM_WRITE);
> +		set_huge_pte_at(mm, addr, pte, entry);
>  	}
>  
>  #ifdef CONFIG_MMU_NOTIFIER
> -- 
> 2.27.0
> 

Re: [PATCH] mm/damon: Use set_huge_pte_at() to make huge pte old

[Muchun Song]

On Mon, Jun 20, 2022 at 10:34:42AM +0800, Baolin Wang wrote:
> The huge_ptep_set_access_flags() can not make the huge pte old according
> to the discussion [1], that means we will always mornitor the young state
> of the hugetlb though we stopped accessing the hugetlb, as a result DAMON
> will get inaccurate accessing statistics.
> 
> So changing to use set_huge_pte_at() to make the huge pte old to fix this
> issue.
> 
> [1] https://lore.kernel.org/all/Yqy97gXI4Nqb7dYo@arm.com/
> 
> Fixes: 49f4203aae06 ("mm/damon: add access checking for hugetlb pages")
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>

The changes make sense to me.

Reviewed-by: Muchun Song <songmuchun@bytedance.com>